1. Field of the Invention
The present invention pertains to nozzle design, more particularly to the nozzle design of rocket motors, and most particularly to a rocket motor nozzle design that uses injected gas to form the xe2x80x9cthroatxe2x80x9d of the nozzle in order to alleviate erosion problems with traditional nozzle designs and allows the use of higher performance propellants within rocket motors.
2. Description of the Related Art
Rocket motors operate by generating large amounts of hot gases from the combustion of a propellant formulation. These combustion gases generate enough pressure within the rocket motor to force the gases out of any exhaust port at high velocity, thus producing thrust. However, for efficient conversion of the enthalpy of the combustion gases into kinetic energy, the exhaust port normally is a divergent/convergent nozzle with a restrictive orifice or throat area. The ratio between the area at the exit plane of the nozzle versus the area at the throat establish how efficiently the nozzle coverts the pressure in the mass flow stream to thrust produced by the rocket motor.
One of the major problems associated with current nozzle designs is that the throat of the nozzles are particularly susceptible to erosion as a result of hot combustion gases and other additives to propellants, such as metal particles to increase energy, as they flow through the nozzle. Many inventions have attempted to address this problem through the use of various erosion resistant coatings and materials, with limited success. Examples of such inventions are disclosed in U.S. Pat. No. 6,086,692, which describes advanced designs for high pressure and high performance solid propellant rocket motors, and, U.S. Pat. No. 6,209,312, which describes rocket motor nozzles having erosion-resistant liners. Due to the limitations inherent in using coatings and materials to address this problem, rocket motor designers are still forced to sacrifice performance by using propellants that do not provide maximum output so as not to unduly erode the throat of the nozzle.
A second problem associated with current nozzle designs for rocket motors relates to the inherent physical properties of a fixed-wall throat. In present rocket motors, the pressure within the combustion chamber is determined by balancing the rate of gas generation and the mass flow rate that can go through the nozzle. Because the rate of gas generation is usually proportional to pn, where p is pressure and n is a constant, and the mass flow rate is normally proportional to p, in order for the rocket motor to be stable, n must be less than 1. This condition effectively limits the rate of burning by excluding a large number of propellant formulations which burn at high rates, but for which n greater than 1.
Therefore, it is desired to provide a rocket nozzle having a throat that is not effected by erosion and a throat area that can quickly change in response to spontaneous changes in pressure such as to prevent the motor from developing a runaway pressure when using a propellant for which n greater than 1. This will allow designers to optimize rocket motor designs to produce maximum thrust.
The present invention does not comprise a traditional convergent section in the otherwise traditional convergent/divergent nozzle. The restrictive effect of the throat is produced by injecting gas into the nozzle rather than providing a physical wall restriction. By using a xe2x80x9cgas-wallxe2x80x9d, the present invention obviates the erosion problems associated with present nozzles as described above. Also, by using a gas-wall, the area of the throat can quickly change in response to spontaneous changes in pressure such as to prevent the motor from developing a runaway pressure when using a propellant for which n greater than 1. The present invention thus allows for the use of fast burning propellants for which n greater than 1, so rocket motor performance can be maximized.
Accordingly, it is an object of this invention to provide a nozzle wherein the restrictive effect of the throat is generated by an injected gas.
It is a further object of this invention to provide nozzles with improved erosion characteristics over present nozzles.
A still further object of this invention is to provide a rocket motor with increased performance capability over current rocket motors.
This invention accomplishes these objectives and other needs related to rocket nozzle design by providing a nozzle body with a divergent, but no convergent section, having no fixed-wall throat, that accepts the combustion products from a rocket motor at one end and allows the combustion products to exit at the other end. Means for circumferentially injecting gas radially and orthogonally to the nozzle body creates the effect of the throat of the nozzle wherein the combustion products are accelerated by restricting their flow.